Annuloplasty prostheses, generally categorized as either annuloplasty rings or annuloplasty bands, are employed in conjunction with valvular reconstructive surgery to assist in the correction of heart valve defects such as stenosis and valvular insufficiency. There are two atrio-ventricular valves in the heart. That on the left side of the heart known as the mitral valve, and that on the right side known as the tricuspid valve. Anatomically speaking, each valve type forms or defines a valve annulus and valve leaflets. To this end, the mitral and tricuspid valves differ significantly in anatomy. Whereas the annulus of mitral valve is somewhat “D” shaped, the annulus of the tricuspid valve is more nearly circular.
Both valves can be subjected to or incur damage that requires that the valve(s) be repaired or replaced. The effects of valvular dysfunction vary. Mitral regurgitation has more severe physiological consequences to the patient than tricuspid valve regurgitation, a small amount of which is tolerated quite well. Many of the defects are associated with dilation of the valve annulus. This dilation not only prevents competence of the valve but also results in distortion of the normal shape of the valve orifice. Remodeling of the annulus is therefore central to most reconstructive procedures on the mitral valve. In this regard, clinical experience has shown that repair of the valve, when technically possible, produces better long-term results as compared to valve replacement.
Many procedures have been described to correct pathology of the valve leaflets and their associated chordae tendinae and papillary muscles. In mitral repairs, it is considered important to preserve the normal distance between the two fibrous trigones. The trigones almost straddle the anterior leaflet portion of the annulus. Between the left and right fibrous trigones the mitral annulus is absent (as described by Tsakiris A. G. “The physiology of the mitral valve annulus” in The mitral valve—a pluridisciplinary approach. ed. Kalmanson D. Publishing Sciences Group, Acton, Mass. 1976, pg 21–26). This portion of the mitral valve apparatus is formed by the change of the anterior portion of the base of the aorta into the (so called) sub-aortic curtain, and hence into the anterior leaflet of the mitral valve. A significant surgical diminution of the inter-trigonal distance could cause left ventricular outflow obstruction. Thus, it is highly desirable to maintain the natural inter-trigonal distance during and following mitral valve repair surgery.
Consequently, when a mitral valve is repaired (be it the posterior or anterior leaflet) the result is generally a reduction in the size of the posterior segment of the mitral valve annulus. As a part of the mitral valve repair, the involved segment of the annulus is diminished (i.e. constricted) so that the leaflets may coapt correctly on closing, or the annulus is stabilized to prevent post-operative dilatation from occurring. Either is frequently achieved by the implantation of a prosthetic ring or band in the supra annular position. The purpose of the ring or band is to restrict and/or support the annulus to correct and/or prevent valvular insufficiency. However, it is important not to over restrict the annulus or an unacceptable valvular stenosis could result. As described above, in mitral valve repair, constriction of the mitral annulus should take place only in the area of the posterior section of the valve annulus.
Shortening of the posterior portion of the mitral valve annulus may be accomplished in several ways. Firstly, by implanting a substantially inexpansible ring (smaller in size than the annulus). With this type of device the surgeon must accurately choose the size of ring that will just prevent insufficiency, yet will not cause significant valvular stenosis. Secondly, by using a contractible ring that may be complicated during implantation. This type has the disadvantage that the surgeon must then accurately judge not only the ring size to use, but also how to space the implanting sutures in the ring and the annulus so that, when implanted, insufficiency is minimized, yet there will be no significant valvular stenosis. Thirdly, and preferably, by a substantially inexpansible ring or band that may be contracted only in appropriate segments (and not in the anterior portion). The natural inter-trigonal distance should be maintained, and the anterior leaflet should not be diminished in circumference.
In tricuspid valve repair, constriction of the annulus usually takes place in the posterior leaflet segment and in a small portion of the adjacent anterior leaflet. The septal leaflet segment is not usually required to be shortened.
As described above, both annuloplasty rings and annuloplasty bands are available for repair of an atrio-ventricular valve. Examples of annuloplasty rings are shown in U.S. Pat. Nos. 5,306,296; 5,669,919; 5,716,397 and 6,159,240, the teachings of which are incorporated herein by reference. See, also, Duran C M G, et al. Clinical and Hemodynamic Performance of a Totally Flexible Prosthetic Ring for Atrioventricular Valve Reconstruction, (Annals of Thoracic Surgery 1976;22(5):458–63); and Duran C M G, Repair of Anterior Mitral Leaflet Chordal Rupture of Elongation (The Flip-Over Technique.) (Journal of Cardiac Surgery 1986;1(2):161–66.). A flexible annuloplasty ring has been available under the trade designation “DURAN™” by Medtronic, Inc., Fridley, Minn., USA. In general terms, annuloplasty rings completely encompass both the anterior and posterior portions of the valve annulus. The posterior portion is often diseased or dilated and not well supported by heart tissue. The anterior portion, in contrast, is well supported by surrounding heart tissue. Thus, it is possible that the annuloplasty ring may overtly support an otherwise healthy anterior portion, potentially leading to tissue failure.
Annuloplasty bands, on the other hand, are specifically designed to primarily encompass only a portion of the valve annulus. For example, a mitral valve annuloplasty band is typically configured to encompass only the posterior portion of the mitral valve annulus, thus promoting natural movement of the anterior portion. In addition to facilitating natural movement of the healthy portion of the valve annulus, annuloplasty bands can be implanted more quickly than annuloplasty rings, as fewer sutures are required. Examples of annuloplasty bands are shown in U.S. Pat. No. 5,824,066 and PCT International Patent Publication No. WO 00/74603, the teachings of which are incorporated hereby by reference. While viable, annuloplasty bands present other concerns. For example, if the band is only anchored into friable valve annulus tissue, there is some concern that the band may possibly pivot excessively relative to the valve annulus. Further, the profile (e.g., thickness) of prior annuloplasty bands may theoretically be sufficiently large so as to restrict or disturb blood flow. Thus, a need exists for an annuloplasty band adapted to provide reinforced attachment about the valve annulus, and a holder and a sizer that facilitate implantation thereof.